The present invention relates to a digitizer, and more particularly, to a digitizer having a dielectric layer formed by screen-printing or vacumm-depositing a transparent dielectric material onto a transparent resistor pattern.
Along with a remarkable development of the electronics industry, a variety of attempts have been made to generate a series of signals from electrographic devices. As a matter of course, the industrial demands for such electrographic devices have also been increased with the advancement of such industrial fields as computer graphics, computer aided design (CAD) and computer aided manufacturing (CAM).
A digitizer is one such electrographic element. In general, a digitizer adopts the same manual operative method as that applied in conventional graphic design. Typically, the digitizer has been manufactured with a complicated checkered net grid type electrode structure. While such a net grid type digitizer supplies a precise linear output signal, the manufacturing cost thereof is increased due to its complicated structure and it is liable to be damaged in use. Moreover, from various applications, it has proved to be desirable to manufacture such a digitizer from extremely transparent synthetic material. However, conventional digitizers generally exclude such a factor as transparency. In the meanwhile, in consideration of the above problems, a new digitizer has been developed the configurational characteristics of which are disclosed in detail in U.S. Pat. Nos. 4,650,926 and 4,853,493. In view of the structure, there is a characteristic difference in that the digitizer disclosed in the former patent (U.S. Pat. No. 4,650,926) is structured such that a dielectric layer is deposited on a layer made of material having a predetermined resistance value, and the digitizer disclosed in the latter one (U.S. Pat. No. 4,853,493) is structured such that a resistance layer is deposited on an insulation layer.
FIG. 1 is a schematic diagram of the conventionally applied digitizer based on the structure of the digitizers described above. Referring to FIG. 1, in the conventional digitizer, a display 14 is disposed in the lowermost portion, a laminated layer 13 (or indium tin oxide (ITO) layer) is deposited thereon, and a patternized transparent resistor 12, e.g., ITO is deposited thereon. Also, a glass substrate 11 is disposed on the uppermost portion of the patternized transparent resistor 12. Here, reference numeral 15 denotes a stylus which selects a desired character or a symbol by being moved in contact with the glass substrate 11. Either a flat panel liquid crystal display (LCD) or a plasma display panel (PDP) are generally used as the display 14.
Meanwhile, in such a structure, the electrostatic capacitance between the stylus 15 and the patternized transparent resistor 12 can be expressed in the relationship such that C=.xi..times.A/d. The descriptive diagram for explaining the above relationship is shown in FIG. 3. Here, a reference letter C denotes electrostatic capacitance, .xi. denotes a dielectric constant of glass, A denotes the area of the patternized transparent resistor, and d denotes the thickness of the glass substrate. In the conventional digitizer, the glass substrate 11 is generally made of thick glass to some extent. Therefore, since the electrostatic capacitance between the stylus 15 on the surface of the glass substrate 11 and the patternized transparent resistor 12 is relatively low, the signal-to-noise (S/N) ratio is deteriorated. As a result, it becomes difficult to select the circuit elements for constituting the digitizer and the operational characteristics of the digitizer are also lowered, thereby eventually resulting in reducing the preciseness of the output signal of the display in relation to the input signal of the stylus.